1. Field of the Invention
The present invention relates to a process for preparing a ketone, an alcohol and a hydroperoxide. In particular, the present invention relates to a process for preparing a ketone, an alcohol and a hydroperoxide comprising allowing a hydrocarbon to be in contact with molecular oxygen to obtain a corresponding ketone, alcohol and/or hydroperoxide.
2. Background Art
Hitherto, it is known to obtain a ketone, an alcohol and/or a hydroperoxide by allowing a corresponding hydrocarbon to be in contact with molecular oxygen (hereinafter referred to as xe2x80x9coxygenxe2x80x9d simply) to oxidize the hydrocarbon. For example, a process for preparing a KA oil (a mixture of cyclohexanone and cyclohexanol) by oxidizing cyclohexane with oxygen and a process for preparing a phenylalkyl hydroperoxide by oxidizing an alkylbenzene with oxygen are known.
In these years, a process has been developed, which comprises oxidizing a hydrocarbon with oxygen in the presence of a catalyst which comprises an imide compound such as N-hydroxyphthalimide, or a catalyst which comprises such an imide compound and a metal compound. For example, JP-A-8-38909 discloses a process comprising oxidizing various hydrocarbons with oxygen in an organic solvent using the above-described catalyst. JP-A-9-87215 discloses a process comprising oxidizing cyclohexane with passing an air or a mixture of nitrogen and oxygen using the above-described catalyst in the absence of a solvent.
However, the process disclosed in JP-A-8-38909 is not satisfactory, since their volume efficiency is low and thus the productivity is insufficient, and furthermore the safety of the process is not satisfactory, and the process disclosed in JP-A-9-87215 is not satisfactory either, since a reaction rate is low and thus the productivity is insufficient.
One object of the present invention is to provide a process for preparing a ketone, an alcohol and/or a hydroperoxide with a high selectivity by oxidizing a corresponding hydrocarbon with oxygen, which is excellent in productivity and safety.
As a result of the extensive study by the inventors, it has been found that the above object can be achieved when a hydrocarbon is oxidized with oxygen in the presence of a cyclic N-hydroxyimide and a compound of a transition metal while supplying an oxygen-containing gas in a reaction system and discharging a gas having a specific oxygen concentration from the reaction system, and thus the present invention has been completed.
Accordingly, the present invention provides a process for preparing at least one compound selected from the group consisting of a ketone, an alcohol and a hydroperoxide comprising the step of reacting a hydrocarbon with molecular oxygen in the presence of a cyclic N-hydroxyimide and a compound of a transition metal, wherein an oxygen-containing gas is supplied in a reaction system and at the same time a gas containing about 1 to about 10% by volume of oxygen is discharged from the reaction system.
According to the present invention, the ketone, alcohol and/or hydroperoxide are prepared by oxidizing the hydrocarbon with molecular oxygen in the presence of the cyclic N-hydroxyimide and the compound of the transition metal. In the course of the reaction, the oxygen-containing gas is supplied in the reaction system and at the same time the gas containing about 1 to about 10% by volume of oxygen is discharged from the reaction system.
Examples of the hydrocarbon used in the present invention include saturated alicyclic hydrocarbons (e.g. cyclopentane, cyclohexane, methylcyclohexane, adamantane, etc.), unsaturated alicyclic hydrocarbons (e.g. cyclopentene, cyclohexene, methylcyclohexene, cyclopentadiene, etc.), aromatic hydrocarbons (e.g. toluene, xylene, cumene, cymene, diisopropylbenzene, tetrahydronaphthalene (Tetraline), indane, etc.), and the like. Among them, the saturated alicyclic hydrocarbons are preferable.
As a result of the oxidation of the hydrocarbon, a compound corresponding to the hydrocarbon in which two hydrogen atoms of the methylene group are substituted with oxo groups is obtained as a ketone, a compound corresponding to the hydrocarbon in which a hydrogen atom of the methyl group, the methylene group or the metylidyne group is substituted with a hydroxyl group is obtained as an alcohol. Furthermore, a compound corresponding to the hydrocarbon in which a hydrogen atom of the methyl group, the methylene group or the metylidyne group is substituted with a hydroperoxy group as an hydroperoxide. For example, when a cycloalkane is used as the hydrocarbon, a cycloalkanone, a cycloalkanol and/or a cycloalkyl hydroperoxide can be obtained.
In the present invention, a combination of the cyclic N-hydroxyimide and the compound of the transition metal is used as a catalyst for the reaction of the hydrocarbon and oxygen.
Examples of the cyclic N-hydroxyimide include N-hydroxyphthalimide, N-hydroxynaphthalimide, N-hydroxymaleimide, N-hydroxysuccnineimide, whichmayhave a substituent, andthe like. Examples of the substituent include an alkyl group, an aryl group, a halogen atom, a nitro group, etc. Specific examples of the cyclic N-hycroxyimide include N-hydroxyphthalimide, N-hydroxychlorophthalimide, N-hydroxynitrophthalmimide, N-hydroxynaphthalimide, N-hydroxychloronaphthalimide, N-hydroxymaleimide, N-hydroxysuccnineimide, etc. The cyclic N-hydroxyimides may be used independently or as a mixture of two or more.
The amount of the cyclic N-hydroxyimide may be from 0.0001 to 20 mole %, preferably from 0.001 to 10 mole %, based on the hydrocarbon.
Examples of the transition metal contained in the compound of the transition metal include cerium, titanium, vanadium, chromium, molybdenum, manganese, iron, ruthenium, cobalt, rhodium, nickel, copper, etc. Among them, cobalt, cerium and manganese are preferable.
Examples of the compound of the transition metal include oxides, organic acid salts, inorganic acid salts, halides, alkoxides, complexes such as acetylacetonate, oxoacids and their salts, isopolyacids and their salts, heteropolyacids and their salts, etc. The transition metals may be used in combination of two or more of them.
The amount of the compound of the transition metal used may be from 0.00001 to 1 mole %, preferably from 0.0001 to 0.5 mole %, based on the hydrocarbon.
In the process of the present invention, the reaction may be carried out in the presence of a solvent. Examples of the solvent include nitriles (e.g. benzonitrile, acetonitrile, etc.), organic acids (e.g. formic acid, acetic acid, etc.), nitro compounds (e.g. nitromethane, nitrobenzene, etc.), chlorohydrocarbons (e.g. chlorobenzene, 1,2-dichloroethane, etc.), and mixtures thereof. When the solvent is used, an amount thereof may be at least about 0.01 part by weight, preferably at least about 0.05 part by weight, and may be about 4 parts by weight or less, preferably about 1.5 parts by weight or less, per one part by weight of the hydrocarbon.
In the process of the present invention, the oxygen-containing gas is supplied in the reaction system containing the hydrocarbon, the catalyst, the optional solvent, etc., and at the same time, the gas is discharged from the reaction system.
As the oxygen-containing gas supplied, oxygen gas, an air, or oxygen gas or an air, each of which is diluted with an inert gas such as nitrogen gas or helium gas may be used.
The concentration of the oxygen in the oxygen-containing gas may be at least 2% by volume, preferably at lest 5% by volume from the viewpoint of the reaction rate, and may not exceed 30% by volume, preferably 25% by volume from the viewpoint of the safety.
The supply rate of the oxygen-containing gas may be from 0.001 to 1 mole/hr., preferably from 0.01 to 0.5 mole/hr. in terms of the oxygen, per one mole of the hydrocarbon.
The oxygen-containing gas may be supplied in the reaction system such that the bubbles of the oxygen-containing gas are. dispersed in the mixture containing the hydrocarbon and the catalyst. The oxygen-containing gas may be supplied with a gas-inlet tube or through a nozzle provided in a reactor.
The size of the bubbles is appropriately selected. The bubble size may be made small, preferably to 1 mm or less, from the viewpoint of the increase of the reaction rate.
The concentration of the oxygen in the gas discharged from the reaction system may be from about 1 to about 10% by volume, preferably from about 1 to about 8.5% by volume. Preferably, the average concentration of the oxygen in the gas discharged during the reaction is in the above range. More preferably, the concentration of the oxygen in the gas discharged during the reaction is always substantially in the above range.
When the concentration of the oxygen in the gas discharged is less than about 1% by volume, the selectivity to the desired product such as the ketone, the alcohol or the hydroperoxide is insufficient. When this concentration exceeds about 10% by volume, the selectivity to the desired product is insufficient, and such a high concentration of the oxygen is undesirable from the viewpoint of the costs and the safety of the process.
The concentration of the oxygen can be adjusted by the suitable selection of the kind and amount of the catalyst, the supply rate and oxygen concentration of the oxygen-containing gas supplied, the reaction temperature, the reaction time, the reaction pressure, etc.
The ratio of the oxygen concentration in the gas discharged to that in the oxygen-containing gas supplied is preferably from about 0.04 to about 0.9.
In the course of the reaction, one or both of the supply and discharge of the gas may be carried out discontinuously or continuously, if desired. Preferably, the gas is continuously supplied under a constant pressure, and the gas is continuously discharged to maintain such a pressure.
The reaction temperature maybe from about 70 to about 200xc2x0 C., preferably from 75 to 150xc2x0 C., and the reaction pressure may be from about 0.1 to 3 MPa, preferably from 0.1 to 2 MPa. In the process of the present invention, the reaction may be carried out batchwise or continuously. The reaction can be carried out continuously by supplying the hydrocarbon and the catalyst and at the same time discharging the reaction mixture while supplying and discharging the gas. Thereby, the operability and productivity of the process can be much increased.
A method of post-treatment of the reaction mixture after the reaction may be suitably selected depending on the properties of the products, etc. Examples of the post-treatment are filtration, concentration, washing, alkali-treatment, acid-treatment, etc. Two or more of these post-treatments may be combined, if necessary. The alkali-treatment can regenerate the alcohol by saponifying an ester of the alcohol with a carboxylic acid as a by-product, and also convert the hydroperoxide to the ketone or the alcohol.
To purify the product, distillation or crystallization can be used.
As described above, according. to the present invention, the ketone, alcohol and/or hydroperoxide can be prepared from the corresponding hydrocarbon with, a high selectivity thereto by the process which is excellent in the productivity and safety.